Means for grinding grain



R. T. GENTRY 2,223,931

MEANS FOR GRINDING GRAIN Filed Dec. 9,1937 6 Sheets-Sheet 1 Dec. 3, 1940.

. mm W @rg I 3 an M. 2m 0M m ma LN s. 5 mm m Site Dec. 3, 1940. R. T. GENTRY MEANS FOR GRINDING GRAIN 6 Sheets-Sheet 2 luvs/woe.- RHBRONTGEM Filed Dec. 9, 1937 Dec. 3, 1940. R RY 2,223,931

MEANS FOR GRINDING GRAIN Filed Dec. 9, 1937 'e Sheets-Sheet 3 RHBRo/v TGENTRY Dec. 3, 1940.

R. T. GENTRY MEANS FOR GRINDING GRAIN Filed Dec. 9, 1937 6 Sheets-Sheet 4 INVENTOR RABROH TGENTRY Dec. 3, 1940. R. T. GENTRY MEANS FOR GRINDING GRAIN s Sheets-Sheet s F i le d Dec. 9, 1957 gwucmo v RHBRON TGENTRY Patented 15cc. 3,1940" UNITED STATES PATENT OFFICE MEANs FoR Gnmnmqqmm Rabron 'r. Gentry, w'mston Salem, N. 0.

Application December 9, 1937, serial No. 17* 971 This invention relates to a grain grinding apparatus and more especially to a method and means for gr inding various portions of a grain contains a starchy substance, comprised of globules which have certain yeast qualities when the ground grain is made into bread: A very small amount of grinding. is required for this powdered head portion. If the powdered portion is ground until the remaining flinty and tough portions of the grain are properly ground, the powdered portion would be damaged and consequently when the breadis made from such meal, the desired flufiiness willnot be present.

Furthermore, the tough kernel of some grains does not require as much grinding as the hard' portion, and if this portion is submitted to the same grinding operation as the filnty portion, its

qualities will be damaged, resulting in a defective meal.

2: 1 Therefore, it is an object of this invention to provide a grain grinding apparatus which is capable of grinding each element of a grain according to its hardness and toughness. By, pro-: viding such an apparatus, a meal of a uniform grade is obtained without disturbing any of the valuable cooking properties therein.

It is a further object of this invention to pro;

vide a method andmeans for grinding grain com-' prising first subjecting the grain toa draft of air 3:, to remove loose particles therefrom, then scouring or scarifying the exterior surface of said grain to, loosen any foreign substances, then subjecting the scoured grain to h second draft of 'air to remove these" Pa ticles from the grain,

4 after which each portion of the grain is ground according to its hardness and toughness.

In order to properly grind each element according to itshardness and toughness, it is necessary to employ three mills, one for each element.

of the mills is deposited intoka'single conveyor troughwhich delivers it to a s 1e outlet.

In-conventional cormmills w of stones is used,'which grind all of the elements of. agrain of corn in one operation, there is from re only one set eight to ten pounds of branfor every bushel of corn. By using the improved method, the bran W content has been reduced toone and one-half to two and one-half pounds per bushel. Therefore, it is seen -that I have provided a method and apparatus which will almost completely remove all of the edible quantities from the bran leaving only the skin or hull. In other words, about ten per cent more meal is obtained by using my apparatus and method.

been stated, other objects will appear as the description proceeds when taken in connection with the accompanying drawings, in which:

Figure 1 is a plan view of my invention; 7 Figure 2 is a front. elevation of the left hand portion of Figure 1;

Figure'ZA is a front elevation of the right hand portion of Figure 1;

Figure "3 is a vertical sectional view taken through a lower portion of the mill, along Jthe line 3-3 in Figure 1;

Figure 4 is. an enlarged longitudinal vertical sectional view, with portions thereof broken away, and taken along the line 4-4 in Figure I, Figure-5 is an' enlarged transverse sectional view through the scouring device and taken along theline 5-5 in Figure 1;

Figure 6 is a sectional plan view taken along the line 8-8 in Figure 4 showing the meansfor supporting the lower end of the grindingstone shafts of the mills employed in this invention; 3

Figure 7 is an elevation looking at theleft hand side of Figure 1;

Figure 8 is a transverse vertical sectional view taken along the lines 8 in Figure 1;

side of a grain of corn;

,Flgure 12 is an isometric View showing the opposite side from that shown in Figure 11;

Figure-13 is a sectional view taken along the line 13-43 in Figure 12.

Referring more specifically to the drawings, the numeral I0 denotes a grain of corn (Figures 11, 12 andv 13) whichcomprises a powdered head portion l I, a tough kernel portion l2 and a hard 1 Some of the objects of the invention, having 0 the portion H or the portion l2.

He'retofore, it 'has been the practice in grain mills, especially corn mills, to grind all three of these parts in one operation. As a result, the powdered portion II is ground far too much and l5 the globules therein are broken. The yeast or rising qualities of the bread are thereby greatly damaged. Furthermore, if the entire grain is ground suificiently to give the flinty portion l3 its proper fineness, the tough kernel portion I2 is ground too much.

It is; therefore, seen that there is a great necessity'for providing anapparatus which will grind these individual portions the proper amount, and no more. I have provided an apparatus which will first grind the powdered portion ll, then the tough oily kernel portion l2 and finally the hard flinty portion |3. In other words, the portion which is most easily ground is first processed, then the next portion of a greater degree of so toughness, and finally the hardest portion.

In the drawings, the numeral l8 designates the framework which supports my grinding apparatus. Upon this framework a suitable hopper I9 is mounted in which the grain such as. shown in 3 Figures 11, 12 and 13 is placed after it has been shelled from the cob. Disposed beneath this hopper is a reciprocating screen box 20 which has suitable wire mesh fabrics or perforated members 2| and 22 in the lower portion thereof and 40 over which the grain is passed, in order to allow certain loose impurities and foreign matter to fall therefrom. This screen box 20 has its upper end pivotally secured as at 24 to an arm 25, said arm being mounted around eccentric head portion 45 26 of a vertically disposed shaft 21 (Figures 1, 2

and 7). This shaft is rotatably mounted in bearings 28, which, in turn, are secured to the framework l8. The lower end of the screen box or sifter 20 has a suitable pin 30 pivotally secured 5o thereto as at 3|. This pin is mounted for-horizontal sliding movement in the upper portion of bearing 32, said bearing 32 being rotatably mounted in the upper portion of the upright 33.

, As the shaft 21 is turned it is seen that the 55 eccentric 26 will cause the screen box 20 and its associated parts to reciprocate and thus cause the grain to move downwardly and over the screens 2| and 22, so that the loose impurities which are mixed with the grain will be allowed to fall through the screen. Also since the member 30 is pivotedas'at 3|, and the bearing 32 is pivoted so as to have rotative movement about its vertical axis, a limited universal movement of the screen box 20 can be had about the bear- 85 ing 32 as the eccentric 26 operates the same.

Disposedin the box 20 and near the lower end thereof is a' partition 35, the lower end of which is disposed slightly above the top of wire mesh 2!. .Near this point one of the side walls 70 of, thebox is cut away as at 36 to allow large foreign substances to pass out of the box. The portion of wire mesh screens disposed to thel left of. partition in Figure '1' is subjected to a v suction draft which is produced by fan 38, whose (I intake extends in close proximity to the lower cannot be removed by the'reciprocating screen.

The lower end of screen box. 20 has leading therefrom a suitable flexible hose connection 10 which leads to the lower portion of an elevator 46. This elevator is typical of several elevators used in this invention. A roller 41 is rotatably mounted in the lower end of the elevator as at 48, saidroller having a suitable belt 49 disposed 15 thereon. Belt 49 is also mounted around a second pulley 50 in the upper portion of the elevator (see Figure 1) and has suitable cups 5| located thereon at spaced intervals which are adapted to collect the grain as it is deposited in the lower portion of the elevator and carry it upwardly. The pulley 50 is fixedly secured on shaft 52, said shaft being rotatably mounted in the elevator 46, as well as in other identical elevators whose functions will be presently described.

The shaft 52 has a pulley 53 on the end thereof upon which a belt 54 is'mounted, and this belt extends downwardly and is mounted on a second pulley 55 on shaft 56. The shaft 56 is rotatably mounted in uprights 51, which in turn are pivoted 30 as at 58 to brackets 59 (Figures 1 and 7).

In order to hold each of the uprights 51 in the proper position, a suitable adjustable link 60 is provided which has one end thereof pivotally engaging the intermediate portion of the upright, 35

, and its other end pivotally secured to the bracket 59. The overall length of link 60 may be changed to vary the position of the shaft 56 and the pulleys thereon, and thereby effect an adjustment in the tautness of the belts. The shaft 56 has another pulley 6| fixedly secured thereonupon which a belt 62 is mounted. The belt 62 is also mounted upon another pulley 63 which is fixedly secured on drive shaft 43. It is seen that the elevators receive their power from 'the drive 45 shaft 43 through the members 53, 54, 55, 56, 6| and 62.

After the cereal grain has been-elevated to the upper portion of elevator 46 (see Figure 2) it is deposited into-the pipe or chute 65, which conveys the grain to scouring and scarifying device 66 (Figures 3 and 5).

The function of this scouring and scarifying device is to loosen the foreign substances which have adhered to the grains and thus facilitate 55 the removal'of these substances so that when the grain is finally ground, only the desired elements will be present. This will also remove the root or husk end |5..of'the grain (Figure 12). This device'is supported by 'a cross member 69 which is 60 disposed between elevators l0 and H.

By referring to Figure 5, it will be seen that the outer casing 13 is secured to the cross member 69 by any suitable means such-as bolts 14. Disposed on the interior wall of the outer casing v a serrated plate 15 against which the grain is thrown in order to scarifi the'exterior surface thereof to assist in removing the impurities as well as portion |5.. Secured within the serrated plate 15 and concentric with the casing I3 is a 70 fixed inverted frustrated conical member 16 which has a hole 11 alignment with another hole 18 which is cut inthe cross member 69 disposed thereabove. The exterior of the member 16 has a plurality of projections disposed thereon which are adapted to cooperate with a second set of projections 8|, disposed upon the interior of inverted hollow conical member 82. This member 82 is fixedly secured on the upper portion of a shaft 83 which has'its intermediate portion rotatably mounted in bearing 84, and its lower end supported by a thrust bearing 85. It will be noted that as the shaft 83 turns that the grain, which is introduced'into the holes 18 and 11 from the spout 65, will pass between the conical members 16 and 82 and the surfaces of the grains will be roughened and scarified by means of the projections 88 and 8| and serrated plate 15.

Means have also been provided whereby the distance between the projections 88 and BI may be varied. This adjustment is effected by a pair of vertically disposed rods 88 which have their lower ends penetrating a cross member 81, said cross member being adapted to support the thrust bearing 85 and the shaft 83. The upper end of the rods 86 penetrate supporting member 89 and have suitable nuts 88a threadedly secured on the upper end thereof. By turning the nuts 88a the distance between points 88 and 8I may be varied. It 'should be further noted that the cross member 81 which supports the shaft 83 and the thrust bearing 85, has its ends slidably secured in suitable guideways 98, said guideways being secured to the proximate faces of elevators 18 and 1|.

In order that rotation may be imparted to the shaft 83 and its associated parts,\ a suitable pulley 95 has been fixedly secured near the lower end of said shaft (see Figure 3). Upon this pulley a belt 96 is mounted which belt also is mounted upon a pulley 91 which is fixedly secured on a center mill shaft 98 (Figures 3 and 4). When this rotative movement is imparted to the shaft 83 and conical member 82, the centrifugal force will cause the grains which are introduced into the opening 11 to move radially ofthe-shaft and to be thrown against the interior of the roughened plates 15. These grains will then fall downwardly onto a suitable housing 99 which is secured to the lower portion of the casing 13. A chute I85 leads from housing 98 and is connected to the lower portion of elevator 18,'which elevator is identical in all respects to the elevator 46. From the lower portion of this elevator, the grain is conducted upwardly (see Figure 8) and is delivered' to a spout I81, the lower end of which communicates with the first mill I89. The spout I81 has a suitable throttle H8 disposed therein which may be regulated in order to direct any surplus amount of grain back into the hopper I9 through spout III. The position of this throttie is regulated by means of a suitable crank II2,

disposed on the outside of the spout I81.

By observing Figure 8, it will be seen that the spout I85 has its intermediate portion connected to a suction fan H5, which fan has a drive shaft H6 upon which pulley H1 is mounted. A belt I I8 is mounted on this pulley and also upon another pulley H9, said pulley H9 being fixedly secured around shaft 83.

As the shaft 83rotates, it is evident that the fan shaft H8 will be rotated to cause a suction draft to be applied to the scarified grain as it passes downwardly through the spout I85. This draft will further remove the loosened impurities such as dust, dirt, portion I5, and the like from the grain. After this suction draft is applied the elements of the grain which are left are in condition for grinding by the various mills, which will be subsequently described.

The mill, I89 is mounted on topof supporting framework I28. This mill comprises an outer casing I2I which has cored holes I22 in its periphery and bottom portion thereof (Figures 2, 2A and 4). Disposed within this casing is a second casing I23, the outer periphery of which is spaced a slight distance from the inner walls of casing I2I in order to allow circulation of air therebetween. The casing I23 is adapted to surround the lower grinding rock I24, said rock being fixedly mounted on the upper portion of shaft I25. This rock has a band I25 mounted therearound upon which is secured a pair of spirally disposed vanes I21, said band and vanes being adapted to rotate along with the grinding rock I24 and draw air downwardly into the casing through openings I29.

The upper face of the rock I24 is properly furrowed .to form a grinding surface so that the grain will be properly cracked and ground (see Figure 10). This upper surface, of the rock I24 is disposed near the lower surface of stationary top grinding rock I38, which is fixedly secured in the upper housing I3 I, said housing being adapted to rest upon the lower casing I2I; likewise the bottom surface of rock I38 is notched and furrowed in the same manner as the upper surface of bottom rock I24. A suitable hole I38a is provided'in the center of the stationary rock I38 so that the grain may be introduced from the spout I81 and onto the top of the rotary grinding rock I24, after which the grain will be crushed between the rocks as the lowermost rock rotates. The furrows in the proximate faces of stones I24 and I38 are identical and cut in the manner shown in Figure 10, but when the top stone is superimposed upon stone I24, the acute edges I32a will shoulder against each other (Figure4) The furrows I32 are much deeper'near the center than at the circumference, but the uppermost cutting edges I32a are in the same plane. These furrows are not radially disposed but cut in sections, each furrow being disposed at an acute angle to the radius of the stone. By so grinding the faces of the stones, any hard metallic substance which might accidentally get into the mill will be sheared and pulverized without damage to the stones; consequently the bridge tree I38 can be rigidly adjusted and the lower ston mounted in a non-yielding position.

When the grain is properly ground it is thrown to the exterior of the rock I24 where it falls downwardly into the casing I23 and is expelled therefrom through opening I34 into the spout I35 and onto reciprocating sifter or belt I36. Special attention is called to the function that the spirally disposed vanes I21 perform. When the grain has been ground, it necessarily follows that a great deal of heat is generated. This heat along with the inherent moisture within the grain will create a humidity or a steam which, if not removedtherefrom, will cause the ground grain to become sog y. and thereby decrease its qualities. By providing the vanes I21, air is drawn down through the openings I29 and the proper ventilation is provided.

In order to vary the distance between the proximate faces between the grinding rocks I24 and I38, asuitable bridge I38 has been provided at the lower end of the shaft I25, said bridge being adapted to be mounted for vertical sliding movement in the lower portion of framework I28 (Figures 4 and 6). Th s bridge is supported by a a pair of vertically disposed rods I39 which. pro- -ject upwardly and have their upper ends normal \rods and consequently the bridge I38 and shaft I25 are raised or lowered. The distance between the rocks I24 and I30 within mill I09 must be such that the grains will be only subjected to the light grinding, that is, a suflicient grinding to separate the powdered portion II from the grain without injuring the globules therein. When this grinding is effected, the entire ground mass will be expelled through spout I35 and onto the screen I45 of the reciprocating sifter or bolt I36.

This screen is of such a mesh that the powdered portion II will be allowed to pass therethrough but the other portions of the grain will be retained. The powdered portion after passing through the screen, will fall into box I 46 disposed therebelow, whereas the portions of the grain retained-upon the screen will gradually move downwardly to outlet I41 and then into the spout I48 which leads to the bottom of elevator 11 From the lower portion of the elevator H the mass of cracked grain which is retained on the screen I45 will be elevated and then delivered to spout I50, said spout leading to the upper portion of the second mill I5I. This mill is identical in construction to the mill I09 previously described except that its parts are somewhat larger. Therefore, like reference characters will be given to similar parts and another description will not be made.

Prior to the cracked grain reaching the mill I5I, however, it is subjected to another suction draft which removes additional impurities and root portions I 5 of the grain which may have not been removed. This suction draft is created by the fan II5, heretofore described, which also effects a suction upon spout I50. This fan II 5 has a duct I52 connected thereto said duct also being connected to the intermediate portion of spout I50- The lowermost rock I24 of the mill I5I is driv en by a vertically disposed shaft 98 which has its lower end supported by another bridged tree I38 similar to the one previously described. The rocks I24 and I30 of the mill I5I are so spaced apart from each other that the tough oily portion I2 of the grain will be properly ground. When so ground it is expelled through the opening I 54 and into the spout I55 from whence it is delivered to screen I56 of reciprocating sifter or bolt I36.

The screen I56 is of such a mesh that the oily portions I2, after they have been ground, will be allowed to pass therethrough and fall into the box I46 dipsosed therebelow, whereas, the re-' maining portion, comprising the hard flinty substance I 3, and the skin or hull I4 will be retained on this screen. As the screen continues to reciprocate these retained portions will be delivered to trough I51 from whence it passes into the lower portion of elevator I58 through flexible hose connection I59.

The elevator I58 will elevate this portion of the grain and deliver it to the spout I60 which is disposed directly above the third mill I6I, which is also similar to the mills I09 and I5I just described, except that its parts are made substantially larger than either.

This mill will grind the hard fiinty portions I3 of the grain and the hull or skin I4. When so ficiently ground and these portions will pass downwardly over screen I66. This screen is much coarser than the screen I64 and will allow most of the coarser elements of the grain to fall through. ,After passing through the screen mesh I66, it is delievered to a flexible spout I61 into the lower portion of elevator I68. This elevator has a pair of pulleys I69 and I10 rotatably mounted therein upon which a belt I1I is mounted, the belt I1I having a plurality of spaced cups I13 secured thereto, which collect the mass from the lower portion of the elevator I68 and deliver it again into the mill I6I through a spout I15.

The lowermost pulley I69 has its shaft I16 extending therefrom upon which is also mounted a pulley I11 (see Figures 1 and 2A). This pulley has a belt I18 mounted thereon which is also adapted to be mounted in the pulley I19 of mill shaft I (Figure 4). By so returning the bran and the elements of the grain which have not been properly ground the first time within the mill I6I another opportunity is given the mill to perfect this grinding and consequently, very little, if any, of this same material will fail to pass through the wire mesh I 64 on its second trip. v

If certain particles are too large to pass through the coarse mesh I66, it is allowed to pass out of the lowermost open end of the sifter I65.

Such particles are generally of such a quality that render them unfit for use as a meal.

By referring to Figure 4, it is seen the manner in which the mills may be connected together, so

that they will be driven in unison. The power necessary to drive the mills is first delivered to a pulley I'which is fixedly secured on one end ofa shaft I86, said shaft being rotatably mounted in bearing I81. The other end of the shaft I86 has a. beveled gear I88 secured thereon which meshes with a beveled. gear I89 which is mounted upon the shaft I80 for vertical sliding movement. For this purpose, a suitable keyway I90 is provided in the shaft I80. For example, when it is desired to vary the distance between the rockswithin the mill I6I, it is necessary to-move the shaft I80 up or down relative to the framework I20; consequently, there must be a sliding connection between the shaft I80 and the relatively stationary beveled gear I89.

In order that this vertical movement of the shaft I80 and its associated bridge I38 on the lower end thereof will be allowed, it is necessary to splice the vertically disposed adjusting rod on the right-hand side of the mill (Figure 4) so .that this rod may be moved vertically without any part thereof contacting the stationary bearing I81. This rod has been divided into sections I39b and I390 which are connected together at the bearing I81 by means of a suitable loop I 39d encircling said bearing. This will allow the necessary adjustment to be made without interfering with the bearing I81.

The lowerportion of the shaft I80 has suitable pulley I92 secured thereon upon which belts I93 are mounted. These belts are also mounted upon another pulley I94 on the lower portion of center mill shaft 98. The shaft 98 has a pulley I95 fixedly secured thereon upon which a belt I96 is mounted, and this belt is also mounted upon the pulley: l91on the mill shaft I25. It is seen that as the pulley I85 is rotated, that a rotary motion will be imparted to mill' shafts I80, 98 and I25 to cause the mills to be operated in unison.

Also fixedly secured on the center mill shaft 98 is a pulley 200 upon which belt 20! is mounted and this belt is adapted to be mounted on a sec- The shaft 203 has another pulley 2H1 fixedly secured thereon upon which belt 2 is mounted. This belt is mounted on another pulley 2l2 fixedly secured on drive shaft 43 (see Figures 1, 2 and 7). The drive shaft 43 has a pulley 2l5 fixed thereon, upon which belt 2l6 is mounted. This belt extends upwardly and has a quarter turn therein, and the upper end' thereof is mounted upon pulley 2ll. The pulley 2H is fixedly secured on eccentric shaft 2l8 mounted in.

bearing M9, and fixedly secured on this shaft are eccentrics 220 and 22! (Figures 1, -2 and 7) around which one end of rods 223 and 224 respectively is mounted. These rods have their other ends connected to sifters or bolts I36 and I65, respectively. It is seen, that as the shaft 2l8 rotates reciprocatory motion is imparted to these sifters.

The sifters I36 and I65 are supported by suitable fiexible upright bars or flats 225 (see Figures 1, 2A and 9) which extend downwardly and are secured to the framework.

It will be noted by referring to Figures 2, 2A, 40 8 and 9 that the box I46 into which the ground grain is sifted has a suitable worm conveyor 230 rotatably mounted therein. The end of this conveyor (see Figure 2) has a suitable pulley 23| disposed thereon and on the outside of the box 45 upon which a belt 232 is mounted, said belt *extending downwardly and being also mounted on another pulley 233 on drive shaft 43. When the mill is in operation, the worm conveyor 230 constantly rotates and draws the meal or ground 50 grain to the left hand end of the conveyor and at this point it is delivered into the lower end of a delivery elevator 235 (Figures 7 and 8).

Elevator 235 has pulleys 238 and 23'! rotatably mounted therein upon which a belt 238 travels. 55 This belt has suitable cups 233 fixed thereon at spaced intervals which collect the meal from the lower portion of the elevator 235 and conduct it to delivery spout 240. -The delivery elevator is driven by pulley 24! which is mounted on the 0 drive shaft", said pulley having a belt 242 mounted thereon. The belt 242 is also mounted upon pulley 243 which is fixedly mounted upon a shaft 2, extending from the lower portion of the conveyor 235 and upon which the roller 236 5 is fixedly mounted.

It is therefore seen that I have provided an apparatus which subjects the shelled grain to an initial suction draft which cleans the loose particles therefrom, a scouring device which loosens 70 the foreign'matter which has adhered to the grain and then grinds each ele ent of the grain directly in proportion to its to hness and hardness.

Throughout the specification I have described the operation of the mill in connection with the grinding of corn. It is evident that the mill can be efiectively used in the grinding of other cereal grains whose characteristics lend themselves to the processing of which this mill is capable. In wheat, for example, there is a husk, a heart, a

powdery portion and a small amount of flinty portion. ,It is therefore evident that by minor adjustments the mill can be used for. the processing of wheat, hulled oats, and in fact any type of grain whose characteristics lend themselves to processing in a manner similar to the processing of corn. l

The mills are of progressively larger size for the reason that the harder portions of the grains require a heavier mill, the size of the mill being proportioned to the hardness of the portion of the grain being ground.

In the drawings and specification, there has been set' forth a preferred embodiment of the invention, and although specific terms are employed, they'are used in a generic and descriptive sense only, and not for the purposes of limitation,

the scope of the invention being set forth in the appended claim.

I claim:

Apparatus for grinding grain comprising three mi1ls, a screen bottom trough disposed belowtwo of the mills and being, adapted to receive the ground particles from the first two mills. a sec- 0nd screen bottomed member disposed below the third mill and being adapted to receive the products of grinding from the third mill, means for imparting vibratory motion to the screen bottomed members, a horizontally disposed trough disposed below the two screen bottomed members and having a screw conveyor therein for propelling the meal falling through the screen bottomed members in a direction towards the first mill, the screen bottomed members sloping in a direction opposite to-the travel of the meal in the trough having the screw conveyor therein, whereby the meal from the three mills will be thoroughly mixed, a trough discharging the ground particles from the first mill into the upper end of the first screen bottomed member, the first screen bottomed member having an open pocket separating the screen into fore and aft portions, a pipe leading from the pocket, a conveyor communicating with the pipe for conveying the coarser particles falling into said pocket to the second mill, a pipe and conveyor communicating with the lower end of the first screen bottomed member for conveying the products of grinding from the second mill to the third mill, a spout leading from the third mill for discharging itsgrindings into the upper end of the second screen bottomed member, the lower end of the second screen bottomed member having a pocket therein covered with a screen coarser than that covering the other portions of the bottom for collecting mills.

. RABRON '1'. GENI'RY.

the products of grinding passing through the- 

